U.S. Pat. Nos. 4,823,408 and 4,905,324, disclose a useful electrically actuated incinerator toilet and useful ash pans for use with the incinerator toilet.
Higher efficiency in the use of electrical energy produced by the electric heater of an electrically actuated incinerator toilet is needed in order to reduce the time of incineration or to increase the rate of incineration and hence the capacity of the toilet for reducing the cost of operation, i.e. kilowatt consumption.
Greater efficiency can be achieved by improving the efficiency of the ash pan.
An ash pan formed by an aluminium insert placed into a stainless steel pan has advantages but is also has been found to have several shortcomings if used with a stainless steel pan formed as a single layer.
Aluminum has a melting point around 1170 degree F. but begins to soften at considerably lower temperatures with the result that the sides of the insert under certain conditions can sag and rupture at operating temperatures of the incinerator; in particular, hot spots can develop immediately beneath waste matter which is burning (exothermic). There tends to be corrosion also at the higher temperatures. The overall result is that the aluminum inserts have to be replaced too often if used with a stainless steel pan formed as a single layer.
Aluminum has a relatively high coefficient for heat conduction, i.e. around 0.5 units as compared to stainless steel having a coefficient for heat conduction of about 0.1 units. Copper has the highest coefficient of heat conduction of commonly available material: 1.0 units. Clearly, if the objective is to provide means to pick up heat from side portions of the insert and conduct it to the bottom section underneath the waste, then copper would be much better than aluminum (1.0 to 0.5); however, copper oxidizes rapidly at the temperatures expected during the incineration process. Furthermore, copper is soft and cannot take the physical abuse associated with cleaning and handling of the ash pan during routine maintenance of the toilet and hence must be secured to a stainless steel layer for ash pan purposes. It has been found however that this approach has problems in that gaps occur between the copper and stainless steel which reduces the advantages of the dual layers.